That's Heavy!-How Does Weight Impact Speed

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Objective

Students will be able to express the impact of weight on speed by conducting a simple experiment.

Big Idea

Students have been comparing the speed of different toy cars, now they get a chance to see how weight impacts the speed of these vehicles.

Opening

10 minutes

Materials Needed for Lesson Opening:

  • Two sets of "Hotwheels" Track that can reach from a table to the floor or a board (i.e.-2"x4") that is wide enough to hold two cars and reaches from the table to the floor.
  • A balance scale.
  • Two "Matchbox" style cars.  Test the cars to make sure that the heavier of the two cars is the fastest on the track

The opening of this lesson is very important because it sets the stage for what our investigation will be focusing on.  I want the students to think about whether the weight of an object impacts its speed.  I want to develop critical thinking skills in my students so I set the stage for them to make this connection on their own.  You will note that I do the demo first before I ask them questions.  I structure the lesson to provide important modeling for the students as they proceed with their own investigation.  Even though their investigation will differ slightly from this one, it provide important scaffolding that will allow them to be successful competing their investigation. 

I gather the students around the track and I say to them, We have been working with comparing the speeds of cars.  After our last investigation, we talked about whether the weight of a car makes a difference in how fast the car moves.  I thought it would be fun for us to see if the weight of a car makes a difference in how fast it travels.

I have two cars.  I am going to put them on the track and see which one travels faster.  (I place the cars on the track and we check to see which cars is faster.  We repeat this two more times so we know for sure which car is faster.

Now, it's time for us see which car is heavier or weighs more.  I have a balance scale here.  I will put each car in a basket on the scale.  The side of the scale that goes down will show us the car that weighs more. 

I place the cars in the scale.  We see which one is heavier.  I say to the students, So we compared these cars and we found out that the heavier car went faster.  Do you think that we can say that is always true?  How can we know that there wasn't some other reason that the one car went faster?  Is there some way that we could conduct an experiment to find out? 

We discuss how we could set up an experiment.  I guide the students discussion as to how we could set up our own experiment to determine if the weight of the car impacts its speed. 

Investigation

30 minutes

Materials needed for this portion of the lesson:

  • Two identical "Matchbox" type cars for each group of students (I suggest you use inexpensive ones from a dollar store--see lesson reflection).  Label one car of each set "A" and one"B" using masking tape. 
  • You will also need something that can be used as a track for comparing the speeds of two cars.  A length of board (like a 2" x 4")  that can reach from the edge of a table to the floor for each group or two sets of "Hot Wheels" track that will reach from the floor to the table for each group.
  • For each group, you will need 3 washers or quarters to serve as weight and 3 pieces of masking tape that will be used to adhere the weights to the cars.  I also keep a few extra washers ready in case the weight added is not enough to increase the speed of the car. 
  • You will also need copies of the Weight Experiment Recording Sheet included as a PDF with the lesson.  There are two copies on each page. 

I say to the students, We are going to find out if the weight of the car impacts the speed.  You should have two cars.  One is marked "A" and one is marked "B".  The first thing you are going to do is put both cars on the track and see which one of the cars is faster.  The speed of the cars should be pretty close to the same because the cars are the same, but there might be something that is causing a difference.  It might be the track, so you should switch the cars on the tracks to make sure you know which one is the fastest.  I give the students time to test their cars to see which one is the fastest.  I remind them that the cars cannot be pushed down the track.  I remind them how to use a pencil to hold the cars in place and then lift the pencil to start the cars down the track (See setup).  After the students have identified the car that is the fastest, I have them set the car aside.

I distribute the recording sheet to the students and I have them write their name on it.  I then say to them, We are going to be adding some weight to the slow car to see if we can make it go faster than our fast car (I show them the washers). I want you to make a prediction about how many washers you think you will need to add to the slow car to make it travel faster than the fast car.  Circle one if you think it will be one washer, two if you think you will need to add two and three if you think you will need three washers.    

After the students have made their prediction, I then have them take tape one of the washers on to the slower car. I have them place the cars on the track and run the experiment (See video).  I remind them to repeat the test, switching tracks.  If the slower car is now faster, I have them circle one on their recording sheet.  I let all of the students tape the second weight on to the cars, even if the first washer is enough.  It is fun for them to see the difference in speed once more weight is added.  We then repeat the process adding another washer and a third time conduct the experiment, recording the results when they have enough weight added. 

When the experiment is done, we come together for discussion.

Discussion

10 minutes

After the experiment, I gather the students to talk about what we learned.  I created a simple chart on the Smartboard to collect their data (click here) This could easily be replicated on chart paper or a whiteboard.  I tell the students that it important for scientists to share data that they have gathered and to look at it together to see if they can draw conclusions or plan further investigations based on the data.  I then ask the students some questions as the basis for our discussion:

1.  How did adding weight impact the speed of your car?

2.  Do you think that if we added more weight, the car would go even faster?

3.  I noticed that one of the cars went faster with 2 washers than with 3.  Why do you think that was?  Do you think we would get to a point that we added enough weight that the car would start to slow down?  Why do you think more weight might slow the car down?  How could we design an experiment to test this? 

4.  How big do you think something would need to be to stop the car?  This question will serve as a "springboard" for an upcoming lesson.